This invention relates generally to ink cartridges that require an ink pressure regulator for maintaining a backpressure, that is negative pressure, in an ink reservoir. More particularly, this invention relates to ink cartridges wherein indication of the amount of ink remaining in the reservoir depends on the operation of the pressure regulator.
Ink cartridges that use an ink pressure regulator to indicate the ink level are known. An example of such ink cartridges is a thermal ink jet print cartridge described in U.S. Pat. No. 5,434,603, Hunt, xe2x80x9cInk Cartridge with Passageway for Ink Level Indicator.xe2x80x9d The print cartridge has an ink reservoir in a rigid cartridge housing and provides a visual indication of remaining ink quantity in the ink reservoir. An ink pressure regulator biases the ink reservoir to create a negative pressure therein. During use the reservoir collapses as the ink supply decreases due to differential pressure exerted thereto.
A pair of flexible tape members are cemented or welded, one to each side of the reservoir. The tape members extend generally parallel toward a narrow end surface of the cartridge housing at which they overlap and are viewable through a window. The overlapping relationship of the tape members provides an ink quantity indicium. As the reservoir collapses, the reservoir draws the free ends of the tape members apart to thereby give an indication of the amount of ink remaining in the reservoir.
An example of the ink pressure regulator is described in U.S. Pat. No. 5,541,632, Khodapanah et al., xe2x80x9cInk Pressure Regulator for a Thermal Ink Jet Printer.xe2x80x9d The ink pressure regulator is placed inside a flexible ink bag to form the spring-biased reservoir described above. The pressure regulator includes a bow spring which is sandwiched centrally between a pair of plates and is configured to have substantially linear force/deflection characteristics. The spring collapses to a substantially flat shape to minimize the amount of ink remaining after printing has depleted the ink from the reservoir.
Consistency and accuracy of ink quantity indication depends on the manner in which the pair of plates collapses towards each other. Ideally, the two plates should be kept parallel as they collapse. Although the design of the bow spring ensures to a large extent that the two plates collapse substantially parallel to each other, there are instances when the plates collapse in a non-parallel manner, such as when the print cartridges are subjected to shock. Subjecting a print cartridge to shock may cause the plates to collapse first at a corner or an edge. If the edges of the plates adjacent the tape members collapse first, the ink quantity indicator will be caused to prematurely indicate that the cartridge is empty when in fact the cartridge still has a substantial amount of ink remaining in the reservoir.
According to an aspect of the present invention, there is provided a pressure regulator for maintaining a negative pressure in a reservoir of a cartridge. The reservoir has a pair of walls, at least one of which is moveable with respect to the other. The pressure regulator includes at least a prop plate for propping the moveable wall, the plate having a central axis therethrough. The pressure regulator also includes a biasing means attached to the plate a predetermined distance away from the central axis for urging the plate against the moveable wall to space apart the pair of walls and to allow controlled lopsided collapse of the moveable wall.
According to another aspect of the present invention, there is provided a cartridge. The cartridge includes a housing and a reservoir supported in the housing. The reservoir has at least a first wall moveable with respect to a second wall. An indicator member is attached to the moveable wall and viewable from outside of the housing. The cartridge also includes a pressure regulator supported within the reservoir. The regulator has at least a plate for propping the moveable wall, the plate having a central axis therethrough. The regulator also includes an off-axis biasing means attached to the plate a predetermined distance away from the central axis towards the indicator member to urge the plate and thus the moveable wall away from the second wall.
According to yet another aspect of the present invention, there is provided a method of indicating an amount of remaining content in a reservoir of a cartridge. The reservoir has at least a first wall moveable with respect to a second wall. The method includes attaching an indicator member to the moveable wall and propping the moveable wall with at least a plate. The plate has a central axis therethrough. The method further includes biasing the plate at a position that is a predetermined distance away from the central axis for urging the plate against the moveable wall to space apart the moveable wall from the second wall. The moveable wall is allowed to collapse in a predetermined lopsided manner to thereby move the attached indicator member as the content of the reservoir is being consumed.